In the specification, reference will be made to "cone-disk transmissions" since this is the generally used term for infinitely variable transmissions in which disks are movable towards each other to engage a transmission belt or chain therebetween at various and adjustable radial positions. The disks themselves need not be precisely conical, yet the term "cone disk" will be used since they are roughly conical and the term is customary in the field. Thus, "cone disk" is not to be construed in the limiting sense to a mathematical conical surface on the disks, but, rather, a short-term designation.
Cone-disk tranmissions have previously been proposed in which one disk of a pair is fixed on a shaft and the other disk is axially movable with respect thereto. The axial movement can be controlled hydraulically. A belt, but usually a steel-link chain, is looped between two pairs, the steel-link chain being supplied with compression elements extending transversely to the longitudinal direction of the run of the chain, and engaging the respectively facing surfaces of the cone disks for transfer of force between the pairs of cone disks by frictional engagement. Some structures of this type utilize cone disks in which the surfaces of the cone disks are curved, usually part-spherical; the engaging compression elements of the chain likewise are formed with engagement surfaces which are rounded, for example also part-spherical.
The frictional engagement between the cone disks and the compression elements is of high importance in transmissions of this type. The contact point is of particular importance. The operability and lifetime of the transmission is highly dependent on this mutual engagement, particularly in view of heat which is generated, heat transmission and conduction for ventilation, wear and tear on the engaging elements and material fatigue thereof. The torque transmission capability of the transmission system is also highly affected by the frictional considerations, including heat generation and dissipation of the components of the structure.
The spherical shaping of the cone-disk surfaces has the purpose to prevent tracking offset of the connecting chain in drive systems of this type, and specifically an inclined running of the chain. This part-spherical configuration is a simple and effective way, frequently used, in order to compensate for tracking offset of the chain. Other possibilities arise, but the geometric bases which cause tracking offset or tracking errors are effectively avoided in cone disks of such at least part-spherical configuration, which, otherwise, arises in cone disks which have differently shaped surface configurations. While the transmission at one particular transmission ratio may be perfect, as the transmission ratios change, the spherical configuration provides for good resolution of difficulties arising due to tracking offset. The curvature of the surface was developed mathematically by F. W. Simonis--see the referenced publication "Stufenlos verstellbare mechanische Getriebe" ("Stepless Adjustable Mechanical Transmissions") by F. W. Simonis, 2nd edition, 1959, published by Springer-Verlag, pp. 8 to 10.
The cone disks, made in accordance with the referenced and well known mathematical derivation may use steel link chains to connect the pairs of the cone disks. The steel link chains include pressure elements which transfer torque by frictional engagement at their facing end surfaces with the cone disks. These facing end surfaces usually include a circular circumferential line, having a radius which is equal to half of the length of the compression elements--measured transversely to the run of the chain.
The arrangement of the cone disks, as mathematically derived, with chains as described, provides for high specific engagement pressure at the contact points. High torque transmissions of this type may, in operation, but subjected to the formation of grooves on the cone disks; the wear of the chain contact elements is substantial. Formation of grooves in the cone disks increases the surface of the engagement between the pressure elements on the chain, which may result in hydrodynamic slippage, with the well known undesired results thereof; in other words, a continuity or constant value of frictional forces is no longer insured. The spherical configuration or bulging results in an angle of inclination of the cone disks which is less at small engagement radii of the chain with the cone disks than the angle of inclination at a large engagement radius of the chain. Consequently, change in the transmission ratio between the pairs of cone disks while the system is stopped is difficult, or under some conditions even impossible, due to self-locking of the chain against the cone disks. Yet, it is frequently desirable to be able to adjust the transmission ratio while the system is stopped. The straight run of the chain is obtained, which is desirable; it is made possible, however, only by requiring high specific engagement pressure and consequent substantial wear of the cone disks and the compression elements on the chains.